Hydrocarbon conversion



May 15, 1951 G. A. MILLS HYDRocARBoN CONVERSION Filed Sept. 26, 1946Patented May 15, 1951 7 HYDROCARBON CONVERSION George Alexander Mills,Ridley Park, Pa., as`

signor to Houdry Process Corporation, Wilmington, Del., a corporation ofDelaware Application September 26, 1916, Serial No, 699,383

VThis invention relates to the catalytic conversion of hydrocarbonsunder cracking conditions using a solid cracking catalyst, and isparticularly concerned with the maintenance of the cracking catalyst atan emcient level of catalytic activity.

In the catalytic conversion of hydrocarbons under cracking conditions,hereafter referred to as catalytic cracking, the original hydrocarbonsare converted to hydrocarbons of different molecular weight or structureor both by contact with a cracking catalyst, which directs andaccelerates the cracking reaction and concomitantly accumulates adeposit of hydrocarbonaceous material commonly referred to as coke.Since the accumulation of such a deposit on the catalyst diminishes itsefficiency and since this effect increases as the amount of the depositincreases, it is the common practice in moving catalyst systems tocontinue the cracking or on-stream period until the catalyst accumulatesa deposit of coke which contains carbon to the total amount of about lto 20 grams per liter of catalyst. (Since the carbon content isconveniently determined, the amount of the coke deposit is generally, asit is herein, referred to its carbon content; as herein used, the amountof the coke deposit is `expressed as grams of carbon per liter ofcontact mass which has been abbreviated to grams per liter.)

When the catalyst is employed as a static bed cooled by indirect heatexchange, the total amount of the coke accumulated is generally somewhatless, usually being of the order of to grams per liter. Thereafter, thecatalyst is treated to remove the majority of the deposit on thecatalyst by combustion during a regeneration period by contacting thecoked catalyst with an oxidizing gas. Due to the difficulty of removingthe last portion of the deposit, the catalyst is generally notcompletely regenerated. After the termination of the regenerationperiod, the catalyst, in commercial practice, generally has a deposit ofless than 1 to 3 grams Aper liter for moving catalyst systems and aboutthe same amount for the above type of static bed operation. Under theseconditions, the catalyst is sufficiently restored to an efficient levelof activity as to be ready for reuse in the cracking operation.

The cracking catalysts commercially available for use in the cycle of`operations described above have certain properties such that there isonly a gradual loss in catalytic activity under the moderate conditionscommonly employed in 7 Claims. ,(CL196-52) the various phasesof thecracking process. If.

however, these catalysts are subjected to an atmosphere containingsteam, a considerable loss in catalytic activity occurs, the extent ofthe loss in activity depending, for a given tempera` t'ure and length1of exposure, on the partial pressure of the steam. Since steam isfrequently used to aid in the volatilization of high boiling hydrocarbonfractions and hence is present during the cracking period, and iscommonly used to strip or purge volatile hydrocarbons from" the catalystprior 4to regeneration, most catalysts are slowly deteriorated or agedin use during the cracking and purging periods and must be replaced withfresh catalyst when the activity has dropped to an'ineflicient level.

Aging 'of'cracking catalysts is also causedby the steam formed in thecombustion of the hy-` drocarbonaceous deposit or coke which consistsessentially of carbon and hydrogen (a typical deposit `contains about 5to 8 weight per cent of hydrogen with the remainder essentially car,'bon) associated in the form of compounds which are of undeterminedcomposition and which are non-volatile withl steam stripping at tempera`tures of the order of 600 to 1000c F.` Combustion of such a depositproduces ilue gases which contain; particularly in the early stages ofthe combustion of the Vdeposit when `preferential combustion ofthehydrogen of the deposit occurs, an amount of steam sufficient, at theele-' vated temperatures of combustion, to lower the activity -of thecatalyst to economically undesirable levels, this effect beingparticularly` cracking or purging periods, this effect beingparticularly noticeable when clay cracking cata` lysts are used. Forthis reason, it has been the previous'practice to limit the temperaturesat which regeneration is conducted to 1100 F. or

be protected against the deleterious effect, ofdefI activating partialpressures of steam at elevated temperatures, such as temperatures above800 F., by maintaining a substantial amount of cokel Y Present.

rthereon is regenerated at temperatures above 1200 F., such astemperatures in the range of 1200 to 1350 F., without substantial lossin activity by contacting such a catalyst with an oxidizing gas undercombustion conditions, said catalyst having been subjected to priorprocess conditions such that sucient coke, such as amounts in excess of15 grams per liter, hasV been deposited on the catalyst as to maintain aprotective amount of said coke on said catalyst during those portions ofthe regeneration period when deactivating partial pressures of steam areSince the deactivating effect of the steam depends, among othervariables, on the temperature of the operation and partial pressures of0.1 pound per square inch or lower can deactivate at temperaturesof 1200F. and higher, it is preferred to protect the catalyst by a minimumamount of coke which varies according to the temperature of theoperation as hereinafter described. Research has indicated that, byoperating the cracking operation under conditions such that the totalamount of coke present on the catalyst at the start of regeneration ishigher than that formerly used, the regeneration may be effected athigher temperatures than previ ously thought desirable. The increase inthe temperature of regeneration has many important advantages, amongwhich is a greatly increased rate of combustion as well as a lowerevolution of heat and decreased amounts of oxidizing gas needed for thesame amount of carbon removed, the latter effect being due to anincrease in the ratio of carbon monoxide to carbon dioxide in the fluegas. These advantages may be realized in a preferred embodiment of thepresent invention, in which the amount of coke on the catalyst at thestart of a combustion effected at substantially atmospheric pressure andat temperatures of 12009 F. or higher is 30 grams per liter or higherand the catalyst accordingly protected in the presence of the partialpressures of steam in the initial stages of combustion (about 1.5 to 3.0or even as much as 4.5 pounds per square inch). As the regenerationproceeds. the amount of cokedeposit, and hence its protective eiect, isvreduced but the concentration of steam in the flue gases decreasesrelatively more rapidly. Thus, although the concentration of steam inthe flue gases (due to combustion of the coke deposit) may be as high as15 or 20 or occasionally as much as about 30 volume per cent during thefirst third of a regeneration effected in connection with a stablecyclic operation, it is generally lower than 5 to 8 volume per centduring Ysecond third of the regeneration. However. it has been foundthat the deactivating effect of gases having concentrations of steam ofeven 5 volume per cent (about 0.8 pound per square inch partial pressureof steam) is appreciable at 1200 F. if the period of exposure issufficiently extended and it is therefore preferred to malnduringregenerations at 1200 F. and higher until the partial pressure ofl steamin the ue gas is:

less than about 0.8 pound per square inch.V Since investigation hasshownV that 15 to 20 grams per liter of the hydrocarbonaceous depositprotects commercial cracking catalysts against the deactivating effectof steam at 1200 F. at least as much as does 6 to 8 grams per liter at1050 F., the advantages of a regeneration effected at the highertemperature may be maintained even in the later stages of a regenerationof a catalyst initially having a deposit amounting to at least 3Q gramsper liter without sacrificing the activity of the catalyst.

In another embodiment of the invention, the deactivating effect of steamused in the cracking period is minimized by maintaining a protectivedeposit on the catalyst during this period. This may be accomplished byincompletely regenerating the catalyst and leaving a residual depositsufficient to protect the catalyst in the subsequent operations, aparticularly eifective amount being in excess of about 10 grams perliter. It has been found that, when steam is preesnt in deactivatingamounts, the advantages gained by the protective effect of deposits ofcoke in excess of l0 to l5 grains per liter more than offsets any lossin the cracking activity of catalysts having such deposits. Furthermore,as the amount of coke on a cracking catalyst is increased above about 20to 25 grams per liter, additional reduction in cracking activity is at.a reduced rate whereas the protective effect of such deposits in regardto the deactivating effect of steam continues to increase. Moreover, theloss in cracking activity due to the deposit of coke on the'icatalystmay be counteracted by increasing the severity of the crackingconditions (increasing the temperature or pres.- sure or decreasing thespacey velocity and the like) or by the use of avery active catalystsuch as aV catalyst which,l Without the deposit of coke, would overcrackthe charge stock, and produce excessive quantities of gas and coke;

For example, in crackingk operationsr involving the contact of acatalyst with hydrocarbons admixed with deactivating. amounts of steam,such as amounts between 5 to .20 parts by weight of steam to 100v partsof hydrocarbons, at temperatures of 950 to 110,0.o the pressure of theoperation being approximately atmospheric (these conditions correspondto about 6.0 to 10.0 pounds per square inch partial pressure of steamfor most hydrocarbon charge stocks), it is preferred to, subject thecatalyst to prior operating conditions, such as prior contact withhydrocarbons or prior partial regeneration, so that atleast l5 grams perliter of coke is initially on the catalyst when it is contacted withsuch deactivating amounts of steam.v Larger initial amounts of coke arepreferred `for the higher Vconcentrations of steam or highertemperatures of cracking or both. Where lower temperatures, such as 800to 950 F. are` employed in the cracking operation,

a minimum deposit ofthe order of grams per conium, magnesium, uranium,beryllium and the like. Other synthetic colloidal masses such asphosphates of zirconium, cerium, 'thorium and theli'kel may beused. Inany event, the utility of a cracking catalyst may-.bey evaluated by astand-Y ardized activity test. and it is preferred, in the.

present invention, to use catalysts of moderate or high activity, suchas catalysts having activities of greater than 25 and preferably above30.

The activity test mentioned above is a standardized test for thecharacterization and control of cracking catalysts and is used by anumber of industrial laboratories. It is known as the CAT-A test and isdescribed in Laboratory Method for Determining the Activity of CrackingCatalysts by J. Alexander and H. G. Shimp, page R-537, NationalPetroleum News, August 2, 1944. In accordance with the method, astandardized light gas oil is subjected to contactwith a static bed ofthe catalyst to be tested understandard cracking conditions ofatmospheric pressure, 800 F. and a rate of oil flow of 1.5 volumes oiliquid oil per volume of catalyst per hour. The cracked products arecollected and analyzed to obtain the activity index, or CAT-A activity,which is the volume of motor gasoline produced divided by the volume ofcharge stock times 100. The Weight per cent of the uncondensed gas andcoke (carbonaceous deposit) as well as the specie gravity of the gas arealso determined.

The above described test is used to evaluate the effect of severeprocess or accelerated conditions; thus, the activity of a sample of acatalyst which has been calcined using no steam, at 1050 F. in flowingdry air for two hours A(hereafter designated as a dry calcination), maybe compared with the activity of a sample of the same catalyst which hasbeen calcined in the presence of a high partial pressure of steam atelevated temperatures as, for example, at 1350 F. for four hours usingabout `15 pounds per square inch absolute pressure of steam (hereafterdesignated as a steam calcination) Evaluations of the effect of processconditions based on the above and similar calcinations have beencompared with data on commercial catalysts which have been in commercialuse for many months or even years and the comparison shows that thesecalcinations can be used to measure the relative effect on crackingcatalysts of prolonged exposure at temperatures of 700 to 1500 F. to thequantities of steam encountered in commercial cracking operations.

Multicomponent refractory oxide cracking catalysts, such assilica-alumina catalysts, which show less than a 50% reduction in CAT-Aactivity between samples subjected to the above described dry and steamcaloinations based on the rst named sample (i. e., 100 times theactivity of the dry calcined sample minus the activity of the steamcalcined sample divided by the activity of the dry calcined sample) areconsidered to be steam resistant and have a satisfactory commercial lifewhen regenerated according to the present invention. As an example ofthe effect of the coke deposit, a catalyst which showed a reduction ofabout 25% in activity between dry and steam calcined samples showed areduction ci only about 13% when the catalyst used for the steamcalcination had a deposit of coke, atY the start of the calcinationamounting to 16 grams per liter. Similar results have been obtained fordifferent amounts oi coke deposit and for dilerent process conditions.

Many of the advantages of the present invention may be realized in anembodiment thereof in which the catalyst is protected during a portionof the cracking period when deactivating amounts of steam are present bycontacting the catalyst prior to such a portion of the cracking periodwith hydrocarbons under cracking conditions selected to provide aprotective amount of cckedeposit. Thus, in the rst portion of thecracking period, the cracking catalyst, which is preferably of moderateor high activity, is contacted in a first cracking zone with arelatively low boiling charge stock, which preferably completelyvolatilizes substantially at the temperature of cracking without the aidof steam, and a protective amount of coke, such as an amount greaterthan 15 grams per liter, thereby deposited on the catalyst. The catalystis thereafter immediately contacted in a second cracking Zone with arelatively high boiling charge stock in the presence of deactivatingpartial pressures of steam, the steam being used to aid in thevolatilization of the charge stock. If the relatively high boilingstock. is sufficiently easily cracked, the cracking conditions in therst and second cracking zones, which zones may be in the same ordifferent reactors, may be essentially the same. ,Howeven ifadvantageous, conditions in the second Zone may be made more severe byincreasing the temperature as by mixing catalyst from the rst zone withhot partially regenerated catalyst having a protective coke depositthereon. Other methods, such as increasing the pressure or decreasingthe space velocity or increasing the catalyst to oil ratio, may also beemployed for increasing the severity of cracking. After passage throughthe second zone, the catalyst may be regenerated wholly or partially,such as being regenerated until 4 to 6 grams per liter oi deposit;remain, and thereafter reused in the same process. By this process, theuseful life of the catalyst is prolonged by the protective effect of thecoke deposit during both the cracking and regeneration periods, while ahigh yield of cracked products are obtained from various fractions of acrude cil, such fractions having different boiling ranges, by crankingeach of these fractions under cracking conditions selected to give theoptimum yields for such fraction. By this process, the benecial effectof steam in the volatilization of charge stocks may be utilized whileminimizing or avoiding the deleterious effect of steam on the catalyst.

In order to understand the invention more fully, reference should be hadto the drawing which illustrates an embodiment of the present invention,which invention is not, however, limited in scope thereto. Fig. 1 is aschematic flow diagram in which details of conventional auxiliaryequipment have been omitted for clarity and which will be described inconnection with operations in which a fluent refractory contact mass iscyclically circulated in a system known as the T. C. C. system. Detailsof this system, as applied to cracking operations, have been describedin various published articles (see, for example, The T. C. C. CatalyticCracking Process for Motor Gasoline Production by R. H. Newton, G. SQDunham, and T. P. Simpson, Transactions of the American Institute ofChemical Engineers, volume 4l, page 215, April 25, 1.945, and thearticles there cited) and hence will not be repeated here. Although thedrawings exemplify one type of moving contact mass operation, thepresent invention can be embodied in other types of operations which usefluent solid Contact masses or may be embodied in that type of operationknown as xed bed operation.

In Fig. 1 a cracking catalyst, such as a lowalkali contentsilica-alumina gel having a mol ratio of silica to alumina of betweenabout 5 to 1 and 15 to 1, is fed from hopper 5 by catalyst leg 6 toreactor 'l Where the catalyst is contacted with' a light. charge stock,such as a virgin or cracked naphtha or gas oil having a dew point atatmospheric pressure below the temperature of cracking in reactor 1, thelight charge stock being introduced to the reactor by line 8r afterhaving been previously vaporized. The catalyst, as introduced to reactorl, is preferably a high activity catalyst, such as a catalyst having aCAT-A activity of greater than 30 and preferably greater than 35, andpreferably has a low coke deposit, such as less than 4 to 6 grams perliter, such as 2 to 4 grams per liter. The charge stock is cracked bysubjecting it to cracking conditions such that at least 35 andpreferably 40 or more volume per cent of gasoline based on the chargestock is produced. Such cracking conditions are generally included inthe ranges of 800 to 950 F.; atmospheric and higher pressures up to 100pounds per square inch; ratios of the liquid volume of charge stockcharged per hour to bulk volume of catalyst circulated per hour of 0.1to and space velocities (ratio of the liquid volume of the charge stockcharged to the reactor per hour to bulk voliune of catalyst in crackingzone) of 0.1 to 5.0. Alternatively, the charge stock f may bea virgin orcracked gasoline, which is reformed to yield a high octane gasoline,such as a gasoline of over 70 octane number. In any event, the catalystaccumulates a protective coke deposit by remaining in the reactor for alength of time (which is called the residence time) such that, under thecracking conditions employed in reactor l, the catalyst accumulates adeposit greater than about grams per liter but generally less than gramsper liter. The catalyst is then .conveyed by line il to reactor 9 whereit is contacted with a relatively high boiling charge stock, such as ahydrocarbon fraction having a dew point of over 800 F. as, for example,a crude residuum from which the tar has been removed. The relativelyhigh boiling charge stock, which is introduced to reactor 9 by line l2after having been heated to a suitable temperature, is admixed with hightemperature steam from line I3 in order that the steam may aid in theVolatilization of the charge stock. The charge stock which is preferablysubstantially completely in the vaporrphase as it enters reactor 9,passes upward through reactor 9 and is at least partially cracked bycontact with the downwardly moving catalyst. The cracked charge stock orsynthetic crude is removed from reactor 9 by line I4 and conveyed to afractionation system for the separation of various products such asgasoline, solv .vent naphtha, fuel oil, recycle gas oil and the like. Ina similar fashion, synthetic crude from reactor l' is conveyed to thesame or a similar fractionation system by line i5 for similar treatment.

The temperature of the catalyst in reactor 9 may be'increased abovethetemperature of the catalyst in line il by mixing the catalyst fromrreactor l with catalyst from line I6, which catalyst has been partiallyregenerated in regenerator Il and thereby increased in temperature. Theamount of catalyst from line l5 used in reactor 9 will depend on therelationship of the temperatures in reactor l, regenerator Il andreactor 9 but it is generally preferred to use an amount of catalystsuch that the temperature of reactor 9 is raised so as to produce atleast 30 and preferably over Yvolume per cent of gaso- Y line from thecharge stock. The temperature rise of the catalyst from reactor l Willgenerally be of the order of V50" to 150e F. In this manner, heatproduced as av result of the regeneration ofthe coked catalyst isutilized in connection with the cracking operation and serves to balancethe endothernricr effect of the latter. The catalyst in line I6 has beenpreferably regenerated so that the coke deposit thereon is about equaltothat on the catalyst in line Il (i. e., about 15 to 25 grams perliter) and isl thereby likewise protected against the steam encounteredin reactor 9 in which reactor the steam concentration may range from 5to 20 parts by weight of steam to 100 parts of oil at 1 to 2atmospheresY or slightly higher total pressure (i. e., arange of 6 to 20pounds per square inch partial pressure of steam). By maintaining atleast 10 grams per liter of coke on the catalyst and preferably 15 gramsper liter or more if the partial pressure of the steam is above 10lpounds per square inch, the deactivating effect of the steam present inthe reactor is diminished. Thus,. for example, a catalyst subjected to15 pounds per square inch partial pressure of steam at 900 F. has 2 ormore times the life (for the same reduction in CAT-A activity) when itis protected with 15 grams per liter of coke than it doesV when theamount of coke is maintained at the usual level of 4 to 6- grams perliter..

The catalyst, which after passage through reactor 9, has a coke deposittotaling preferably at least 25 and generally about 30 to 40 grams' perliter or higher, is removed from reactor 9 by line I8, and conveyed toelevator I9 which carries` the catalyst to line 2 lv and thence tohopper 22. The catalyst is fed from hopper 22 by line 23 to regeneratorl1 which may be a T. C. C. kiln comprisinga plurality of burning andcooling sections or zones (twor of which are shown in regenerator Il). Acontrolled amount of air from` manifold 24 burns some of the cokedeposit in each section of the kiln, the spent flue gases being removedby manifold 25. Excess heat generated by combustion of the coke depositis removed by indirect heat exchange, using cooling coils 26. Theconditions of combustion in regenerator Il and the temperature of theair used therein are selected so that the heat of combustion soon raisesthe temperature of the catalyst to greater than 1100 F., such as a;temperature in the range of 1200 Vto 1350 F. The safetemperature ofcombustion is dependent onthe amount of the coke deposit on the catalystas introduced to the regenerator, and the lower temperatures, such asabout 1200 F., are preferred'when the amount of the coke deposit isabout 30 grams per liter whereas higher temperatures, such as l300 orhigher, may be employed when the coke deposit is in excess of 40 gramsper liter.

The catalystaf,ter partial regeneration, may be conveyedy fromregenerator 'l by line 2l to regenerator 28, `which'is similar in designto regenerator il, and additional regeneration effected. Alternatively,a single regenerator with'appropriate arrangements for the draw off ofcata..

lyst may be used. AsV noted above, the hydrogenV below the temperatureof thermal deactivationY for the particular type of catalyst employed.

The temperature of thermal deactivation of a catalyst is the temperatureabove which rapid deactivation occurs in a non-deleterious atmosanatra9V phere, such temperatures being, for example, about 1500 F. for claycatalysts and about 1700 F. for synthetic silica-alumina catalysts. Ingeneral, the same temperature of regeneration in both regenerators iscorrelated with the amount protects the catalyst in the subsequentregeneration. The catalyst from the mixed phase operation may bepartially regenerated so as to leave a coke deposit of at least 15grains per liter and thereafter reused in the mixed phase cracking ofprotective coke deposit and the partial presoperation. sure of steam. Ithas been found by investsa- After extended periods of use, mostcatalysts tion that steam resistant catalysts (as defined are unavoidamyaged, 1n this event, the amount above) will have a satisfactorycommercial life of the coke deposit maintained during the crackwhen theminimum amounts of coke given in the ing period may be decreased with aconsequent table are observed at the stated partial pressures increasein the catalytic activity. Thus, in a comof steam. i mercial processoperated continuously, by start- Table Temp Amount of Partial Amount ofPartial Amount of Partial Coke Pressure Coke Pressure Coke Pressuregrams per Ibla/sq. grams per Iba/sq. grams per Iba/sq.

liter inch liter inch liter inch 1,15o F 1o s. 9 is 4.4 1,2oo F 15 1.51s 3.9 23 4.4 1,a0o F 23 1.5 26 3.9 so 4.4 1,35o F en 1.5

It is, however, preferred, according to the invening with an over activecatalyst on which suffition, to have the minimum coke about high- 25cient coke is maintained during both the cracking er than the valuesgiven in the table to provide a and regeneration phases so as todecrease the factor of safety and to allow for the reduction of agingeffect of steam present during these and the coke deposit during theregeneration. other process periods, the useful life of the cata- 'Ihecatalyst, after being regenerated so as to lyst can be extended,particularly when the leave a predetermined residue of coke deposit .mamount of coke maintained on the catalyst durthereon, is removed fromregenerator 28 by line ing the cracking period is reduced as the aging29, conveyed by elevator 3| to line 32 and thence of the catalystproceeds. charged to hopper 5 from which it may be re- It is to beunderstood that where the term, moved for reuse. partial pressure ofsteam, is used that such an In another embodiment of the invention, avery expression includes those instances Where steam high boiling chargestock, such as a residuum is essentially the only vaporous materialpresenty having an end boiling point of greater than 1100 and thepartial pressure of steam is hence equal F. and a mid boiling pointbetween 800 to 1100" to the total or absolute pressure of the system. F.at atmospheric pressure is charged in a mixed f Obviously manymodifications and variations of phase condition to a cracking catalysthaving a the invention as hereinbefore set forth may be protective cokedeposit, the catalyst being at a made Without departing from the spiritand. scope temperature generally higher than vapor phase thereof andtherefore only such limitations operations, such as temperatures in arange of should be imposed as are indicated in the ap- 900 to 1l00 F.Typical charge stocks employed v pended claims. in such mixed phaseoperations are commonly ad- I claim as my invention: mixed with about 5to l0 parts by weight of steam 1. In a catalytic cracking system inwhich to 100 parts of charge stock prior to the heating fluent solidcracking catalysts contacts substanof the charge stock to thetemperature of introtially only hydrocarbons in a first stage crackingduction to the cracking zone, generally about operation and contactshydrocarbons and sub- 700 to 950 F., in order to prevent coking 0f 50stantial amounts of steam in a second stage the charge stock in the tubestills used for heatcracking operation, the improvement which. comingThe deaCtVatng effect 0f the Steam adprises maintaining crackingconditions in said mlXd With the Charge Stock (Which, for the Op' rststage cracking operation so as to deposit an eratlon described above,amounts to partial presamount of Coke on, substantially Completely re-,Sures of from about 7'0 to 10'0 pounds Per square 65 generated calatystsufficient to furnish substanmh) at tpe tempratures of the crackmg Opertial protection to said catalyst against the deactialol (90o go t100 F),I nay be decreased by em' vating effect of steam in said second stageIlconsoymg ta fe teb.' actlvTckffg Caalst Sfucl tacting a'm'ixture ofcatalyst from said first stage l a ca a ys avmg a ac 1V? y o a andpartially regenerated catalyst comprising an east 30 and preferably atabove 35, which cata- 60 am t f k t 1e t e ual to the coke on Said lysthas a coke deposit amounting to at least 15 Gun o C0 e a s t q .th h d bgrams per liter and preferably in the range of catalyst from the rs5.3%? W1 y Tocar ons m 20 to 30 grams per liter at the start of thecrackthe prseme of a' deactwatmg partlal pressutqe. of. ing operation.When a catalyst is used which is steam m Sald Second stage and therbydgosltm. originally so active that, under the cracking cona'ddltlonala'munts of coke (.m sala nlnxture o ditions employed in the process,overcracking capalyst partlauy regeneratmg Cata ys from would result (i.e., overcracking is the formation Sad Second Stage cmlmg operano S0 asto pro of gas and coke at the expense of gasoline formaduce catalystcomprlsmg an amount of c oke at tion), the coke deposit decreases theactivity of least equal to the? amount O f cle produed m sald theactivity of the catalyst and thus decreases f'st Stag? Crackng Operatlonmtroducmg a pot overcracking while protecting the catalyst against t1onof said partially regenerated catalyst to sa1d the deactivating effectof steam. The catalyst, Second Stage laking Operation, further Tege11-after use in the mixed phase cracking operation v @rating aIlOtheIDOItOIl 0f Said partially regengenerally has a coke deposit-amounting to30 to @rated Catalyst S0 aS t0 pIOduCe Substantially 50 grams per liter,which, as discussed above, 75 completely regenerated catalyst andintroducing weer substantially completely regeneratedl catalyst .to

said Vrst stagecrackingoperation.

A:Zwin a catalytic .cracking system in rwhich fluent solidcrackingfcatalyst contacts substantially only hydrocarbons in aiirststage cracking operation and contacts hydrocarbons and substantialamounts of. steamin aseccnd stage ,cracking operation, the improvementwhich comprises maintaining cracking conditions in ,said rst stagecracking operation so as to deposit an amount of ook-e on substantially.completely regenerated' catalyst suiiicientA to .furnish substantialprotection to said catalyst against the deactivating eiect of steam insaid second stage, contacting a mixture of catalyst from said rst stageand partially regenerated catalyst comprising an amount of coke atleastequal to the coke on said catalyst from the first stage withhydrocarbons in the presence of a deactivating partial pressure of steamin said second stage under such conditions as to deposit an amount ofcoke on said catalyst suflicient to furnish substantial pro- Y, tectionto said catalyst during that portion-of 'l the-subsequentregeneration-when said catalyst is contacted with' deactivating partialApressuresofV steam, partially regenerating catalyst fromV said second-stagecracking operation at temperatures of at least l200 F.under-conditions such` that the coke deposit that remains on saidcatalyst is at least as much as the coke deposit on the catalyst fromsaid rststage operation', in-Y troducing a portion of the partiallyregenerated catalyst to said second stage cracking operation,

further regenerating a portion of the-partially re-v and substantialamounts of steam in a second stage cracking operation,.the improvementwhich comprises maintaining cracking conditions in-said rst stagecracking operation so as to deposit coke to the extent of at least 15grams of carbon per liter of catalyst on substantially completely re,-generated catalyst having a deposit of less than 6 grams of carbon perliter of catalyst, contacting a mixture of catalyst from said rst stageand partially regenerated catalyst comprising Van amount of coke atleast equal to the coke on said catalyst from the iirst stage withhydrocarbons in the presence of a deactivating partial pressure of steamin said second stage under such cracking conditions as to deposit anamount of coke on said catalyst suiiicient to provide at least 15 gramsof carbon per liter of catalyst on said catalyst during that portion ofthe subsequent regeneration when said catalyst is contacted with apartial pressure of steam of more than 0.8 pound per square inch,partially regenerating catalyst from said second stage crackingoperation at temperatures of at least 1200 F. under conditions such thata deposit of coke of more than 15 grams of carbon per liter of catalystremains on said catalyst, introducing a portion ofthe partially re- Ygenerated catalyst to said second stage cracking operation, furtherregenerating a portion oi the partially regenerated catalyst `attemperatures of at least 1200 F. so as to produce substantiallycompletely regenerated catalyst having a coke deposit of less than 6grams of carbon per catalyst is employed in a cyclic processcomprisliter of catalyst and introducingsubstantially completelyregenerated catalyst to said first stage cracking operation.

4. In the catalytic conversion of hydrocarbons using solid hydrocarbonconversion catalyst, which catalyst is employed in a cyclic processcomprising a conversion period and a regeneration period, during whichconversion period hydrocarbons contact said catalyst to form conversionproducts and concomitantly deposit coke on said catalyst and duringwhich regeneration period the coked catalyst is regeneratedby-contacting it with oxygen containing gas under combustion conditionsso as to remove at least a portion of said coke Vwith the consequentpresence- Vof steam in the flue gases present during the regeneration,the steps which comprise contacting said catalystvvith hydrocarbonsduringsaid conversion period and depositing a protective amount of cokeon said catalyst suiicient to` provide a deposit of at least 15 grams ofcarbon per liter of .catalyst during the subsequent regeneration lperiod until the partial pressure of steam-in the nue gases is less thanabout 0.8 pound per square pound per square inch, separating saidpartially; regenerated catalyst and flue gases, contactingsaid partiallyregenerated catalystV withl addi-YA tional oxygen containing gas in asecond regeneration zone, completing regeneration oiV said partiallyregenerated catalyst in said secondjregeneration zone at temperatures ofat Aleast-1200? F. and under conditions such thatl the partialV pressureof steam in the gases present` is less than 0.8 pound per square inchand thereafter-contacting completely regenerated catalyst withhydrocarbons under conversion conditions. Y

5. In the catalytic cracking of Vhydrocarbonsusing solid hydrocarboncracking catalyst, which ing a cracking period and a regenerationperiod, during which cracking period hydrocarbons contact said catalystto form cracked products and concomitantly deposit coke on said catalystand I* during which regeneration period the cokedcatalyst is regeneratedby contacting it with oxygen containing gas under combustion conditionssok as to remove at least a portion of said'coke With the consequentpresence of steam in the flue gases present during the regeneration, thesteps Which comprise contacting said catalyst with hydrocarbons duringsaid cracking period and depositing a protective amount of coke on saidcatalystsuflicient to provide a deposit of at least 30 grams of carbonper liter of catalyst during the subsequent regeneration period untilthe partial pressure of steam in the gases present is less than about1.5 pounds per square inch, contacting catalyst comprising saidprotective amount of Y coke with an oxygen containing gas in a rsttional oxygen containing gas in a second regenff eration zone,completing regeneration of said partially regenerated catalyst attemperatures of at least 1200 F. and under conditions such that thepartial pressure of steam in the gases present is less than 1.5 poundsper square inch and thereafter contacting catalyst so regenerated withhydrocarbons under cracking conditions.

6. In the catalytic cracking of hydrocarbons using solid crackingcatalyst, which catalyst is employed in a process comprising a crackingperiod and a regeneration period, during which cracking periodhydrocarbons contact said catalyst to form cracked products andconcomitantly deposit coke on said catalyst, during which regenerationperiod an oxidizing gas contacts said catalyst under combustionconditions so as to remove at least a portion of said coke, the stepswhich comprise contacting substantially completely regenerated catalysthaving a depositx of less than 6 grams of carbon per liter of catalystwith substantially only relatively light hydrocarbons having a dew pointbelow the temperature of cracking in a first cracking operation anddepositing coke on said catalyst such that the total amount of coke onthe catalyst after said rst cracking operation totals at least 15 gramsof carbon per liter of catalyst, and thereafter contacting said catalystcomprising at least 15 grams of carbon per liter of catalyst with agaseous mixture of relatively heavy hydrocarbons having a dew point ofover 800 F. and steam, said steam having a partial pressure of at least6 pounds per square inch, in a second cracking operation.

7. In a process for the catalytic cracking of hydrocarbons using solidcracking catalyst, the steps which comprise contacting substantiallycompletely regenerated catalyst having a deposit of less than 6 grams ofcarbon per liter of catalyst with substantially only relatively lighthydrocarbons having a dew point below the temperature of cracking in afirst cracking operation and depositing coke on said catalyst such 14that the total amount of coke on the catalyst after said rst crackingoperation totals at least 15 grams of carbon per liter of catalyst,contacting said catalyst comprising at least 15 grams of carbon perliter of catalyst with a mixture of relative heavy hydrocarbons having adew point of over 800 F. and steam, said steam having a partial pressureof at least 6 pounds per square inch, in a second cracking operaticn,contacting catalyst from said second cracking operation with oxygencontaining gas in a rst regeneration zone, eiecting an initial partialregeneration of said catalyst in said rst regeneration zone attemperatures of at least 1200 F. and generating flue gases having apartial pressure of steam of greater than 0.8 pound per square inch,separating said partially regenerated catalyst and flue gases,contacting said partially regenerated catalyst with additional oxygencontaining gas in a second regeneration zone and completing regenerationof said partially regenerated catalyst in said second regeneration zoneat temperatures of at least 1200 F. and under conditions such that thepartial pressure of steam in the gases present is less than 0.8 poundper square inch.

GEORGE ALEXANDER MILLS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,253,486 Belchetz Aug. 19, 19412,290,580 Degnen et al July 121, 1942 2,327,489 Becker Aug. 24, 19432,348,646 Reeves May 9, 1944 2,356,697 Rial Aug. :22, 1944 2,372,018Ruthruff Mar. 20, 1945 2,385,326 Bailey, Jr. Sept. 25, 1945 2,407,914Bailey. Jr., et al. Sept. 17, 1946

6. IN THE CATALYTIC CRACKING OF HYDROCARBONS USING SOLID CRACKING CATALYST, WHICH CATALYST IS EMPLOYED IN A PROCESS COMPRISING A CRACKING PERIOD AND A REGENERATION PERIOD, DURING WHICH CRACKING PERIOD HYDROCARBONS CONTACT SAID CATALYST TO FORM CRACKED PRODUCTS AND CONCOMITANTLY DEPOSIT COKE ON SAID CATALYST, DURING WHICH REGENERATION PERIOD AN OXIDIZING GAS CONTACTS SAID CATALYST UNDER COMBUSTION CONDITIONS SO AS TO REMOVE AT LEAST A PORTION OF SAID COKE, THE STEPS WHICH COMPRISE CONTACTING SUBSTANTIALLY COMPLETELY REGENERATED CATALYST HAVING A DEPOSIT OF LESS THAN 6 GRAMS OF CARBON PER LITER OF CATALYST WITH SUBSTANTIALLY ONLY RELATIVELY LIGHT HYDROCARBONS HAVING A DEW POINT BELOW THE TEMPERATURE OF CRACKING IN A FIRST CRACKING OPERATION AND DEPOSITING COKE ON SAID CATALYST SUCH THAT THE TOTAL AMOUNT OF COKE ON THE CATALYST AFTER SAID FIRST CRACKING OPERATION TOTALS AT LEAST 15 GRAMS OF CARBON PER LITER OF CATALYST, AND THEREAFTER CONTACTING SAID CATALYST COMPRISING AT LEAST 15 GRAMS OF CARBON PER LITER OF CATALYST WITH A GASEOUS MIXTURE OF RELATIVELY HEAVY HYDROCARBONS HAVING A DEW POINT OF OVER 800* F. AND STEAM, SAID STEAM HAVING A PARTIAL PRESSURE OF AT LEAST 6 POUNDS PER SQUARE INCH, IN A SECOND CRACKING OPERATION. 